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From: "mital at mitalashok dot co.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/115476] [13/14/15 Regression]
 __has_unique_object_representation ICE with array of uninstantiated type of
 unknown bound
Date: Thu, 13 Jun 2024 18:14:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115476

--- Comment #7 from Mital Ashok <mital at mitalashok dot co.uk> ---
I think the issue is the same as it was in Clang

The preconditions for `has_unique_object_representations` is
https://eel.is/c++draft/type.traits#tab:meta.unary.prop-row-47-column-3-sen=
tence-1

> T shall be a complete type, cv void, or an array of unknown bound.

Which is implemented in GCC as `check_trait_type (type1, /* kind =3D */ 1)`
https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dblob;f=3Dgcc/cp/semantics.cc;h=3D0=
8f5f245e7d11a76b975bb04c0075ded1b3ca8ba;hb=3D609764a42f0cd3f6358562cab98fc2=
20d3d2d9fd#l12969

However, unlike the other traits with the same preconditions (like
`__is_assignable(T, U)` for both of its type arguments), instead of simply
being `false` when given an array with unknown bounds, it recurses in, so it
implicitly has a precondition that "T is cv void or
std::remove_all_extents_t<T> is complete", which should be checked with
`check_trait_type (type1, /* kind =3D */ 2)`.

`__has_trivial_destructor` also seems to be miscategorized as kind =3D 1 to=
o,
leading to this unintended result:

    struct Foo;
    static_assert(__has_trivial_destructor(Foo[]));
    struct Foo { ~Foo(); };
    static_assert(!__has_trivial_destructor(Foo[]));=